Beech-Birch-Maple 



This forest type, which is also known as the northern hardwood type, is 

 characterized by American beech, yellow birch, and sugar maple. Other 

 common associates are basswood, red maple, red oak, white ash, eastern white 

 pine, balsam fir, cherry, paper birch, gray birch, American elm, slippery elm, 

 hophornbeam, red and white spruce, and hemlock. 



Northern hardwoods are normally found in areas with deep (over 20 inches; 51 

 cm), moist, well-drained soils. In Maine this type is most common in the 

 western and central regions of the State but occurs on mid-elevation sites in 

 eastern Maine as well (figure 9-2). In coastal Maine this type is found mixed 

 with spruce and fir in the mid-coast areas (Casco to Penobscot Bays) and is 

 found inland from the coastal stands of spruce and fir east from Penobscot Bay 

 to Machias. 



This type includes the aspen-birch subtype described by Ferguson and Kingsley 

 (1972), which is an important association on forestland recently disturbed by 

 logging or fire. This is a successional type, however, and gives way to 

 either northern hardwood or spruce-fir, depending on the site. 



SUCCESSION OF FOREST SYSTEMS 



The development of forest vegetation on an area follows a somewhat predictable 

 sequence of changes in plant communities known as succession. Temporary plant 

 communities (grasses, shrubs, and aspen-birch trees) in this process are known 

 as serai stages. Each serai stage modifies the environment in such a way that 

 it becomes more suitable for the invasion of another plant association, which 

 then succeeds the previous one. A plant association that ultimately dominates 

 is known as the climax association. In Maine the climax associations on all 

 land and fresh water habitats are forests. 



Maine's original forests developed after the last glaciation through primary 

 succession on exposed rock, glacial till (soil), or water (figure 9-3). Early 

 serai stages of primary succession (lichens, mosses, and herbs) result in the 

 accumulation of organic matter and mineral soil so that shrubs and then trees 

 eventually are able to survive. The order in which different species of trees 

 invade a site depends on the "tolerance" of each species (table 9-4), as well 

 as on site conditions. Tolerance refers to the ability of a plant, especially 

 a young plant, to survive in an understory (under a tree canopy). A tolerant 

 tree is one that can compete successfully with other plants for moisture and 

 nutrients and can grow well under low light intensity (Spurr 1964) . 

 Intolerant trees, such as birches, aspens, and pines, comprise the first serai 

 stage dominated by trees. Intolerant trees grow rapidly in full sunlight and 

 can outgrow and overtop more tolerant species that are present. Intolerant 

 trees usually have open canopies, which allows more tolerant species to invade 

 underneath the canopy. 



In some areas tolerant tree species (table 9-4) such as red spruce, balsam 

 fir, sugar maple, and American beech, often invade as an understory and form 

 the climax plant association as the overstory trees die out. These species 

 usually succeed themselves because their seedlings survive under the dense 

 shade of closed canopies. Tolerant tree seedlings do not necessarily grow 

 rapidly under heavy shade; they are merely able to survive until they can be 



9-8 



